The 2013 version of Compressed Gas Association (CGA) Standard CGA V-1 specifies 115 cylinder-valve outlet connections for 270 compressed gases. The Standard specifies that all seals are metal to metal. In the Standard, the sealing geometry varies from connection to connection to ensure they can't accidentally be mismatched with an improper gas. Items such as thread size, thread pitch, thread direction, sealing form and angle, pilot bore and pilot length are changed.
FIG. 1 depicts an exemplary, prior-art, Standard cylinder-valve outlet connection: CVGA V-1 Connection 300 (0.825″-114 NGO-RH-EXT, a conical nipple style). In FIG. 1, line A represents a maximum radius of any part of valve with or without outlet cap=1.5 (38.1) with respect to the centerline of inlet thread on valve. FIG. 2 depicts another exemplary, prior art, Standard cylinder-valve outlet connection: CGA V-1 Connection 630 (1.030″-14 NGO-RH-EXT for ultra-high integrity service, a sealing-gasket style). In FIG. 2, line A represents a maximum radius of any part of valve with or without outlet cap=2.08 (52.3) with respect to the centerline of inlet thread on valve. As noted, there are 113 more outlet connections. For each of the 115 connections, CGA V-1 provides the geometry, surface finishes, materials and dimensional values/tolerances to ensure standard fits and proper performance.
The proliferation of connections prevents accidentally connecting inappropriate equipment to a compressed gas cylinder. However, it also makes valves non-interchangeable and unnecessarily expensive and unserviceable. This wastes natural resources and energy, and creates a stocking nightmare. That is, 115 valves are needed to support 270 gases. With some valve forms this stocking problem has forced the gas industry to experience lead times of 6-9 months and to make significant financial investments in inventory to mitigate these lead times and remain competitive.
In addition, in some gas applications, e.g., semiconductor gases where purity is extremely critical, any scratches or damage to the outlet area of the valve provides an area for impurities to be retained. As a result, damage to a valve outlet would cause the rejection of the cylinder and its contents, which would then require the gas supplier to incur significant costs to return the cylinder, remove and mitigate the gas contents, and, in most cases, dispose of both the valve and cylinder; the entire return process potentially costing thousands of dollars per cylinder.
For these reasons it would be desirable to have a common valve (or a small number of valves) and interchangeable outlet connections. This would greatly simplify the manufacturing and stocking of valves.